It is known that reheat furnaces are intended to heat iron and steel products, such as slabs, blooms, billets, blanks or any other semi-finished product in the iron and steel industry, to the temperatures required for rolling.
It is also known that rolling, depending on the nature of the process used or on the final thickness of the finished product to be obtained, requires a heat treatment and a precise hardness of the product to be rolled. For a metal of a given chemical composition, this hardness depends on the temperature to which the product was heated.
The product temperatures required by the rolling operations are characterized by:
the average temperature of the product and PA1 the temperature uniformity of the product, for example between its upper face, its center and its lower face. PA1 a large thermal inertia of the furnace, which limits rapid changes in the temperature of the latter, and PA1 the limited number of regulating zones in the furnace which, especially for construction reasons, does not allow the temperatures over the entire length of the furnace to be controlled precisely. PA1 charging temperature PA1 dimensions or shapes and PA1 steel grades, or PA1 their discharge temperature PA1 the uniformity of the discharge temperature PA1 the presence of black lines PA1 the ignition losses PA1 the creep PA1 the decarburization or PA1 the heat treatment.
Precision in the thermal state (average temperature and temperature uniformity) of the products is imperative for high-quality rolling of steels, particularly high-carbon steels, stainless steels, ferritic and austenitic steels, silicon steels, etc.
The average temperature level is obtained by passing the products through so-called heating zones which are characterized by a large heat influx which produces significant thermal non-uniformity in the products.
The desired levels of temperature uniformity in the products are achieved by passing the products into an equalization zone in which the heat influx is very small, the products remaining therein for a controlled period, thereby allowing the temperatures within the products to be made uniform.
At the present time, the known reheat furnaces for iron and steel products, before rolling, are characterized by:
These two characteristics of the known reheat furnaces limit the flexibility of these furnaces as well as their capacity to reheat, in a continuous fashion, batches of different products, particularly with respect to their physical characteristics of:
batches of different products, particularly with respect to their thermal reheat objective, characterized by: